The present invention relates to the art of selective nerve stimulation. The invention finds particular application in conjunction with urination control and will be described with particular reference thereto. It is to be appreciated that the invention is also applicable to control other aspects of the nervous system, such as for fecal incontinence, penile erection, and others.
The organs involved in bladder, bowel, and sexual function receive much of their control via the second, third, and fourth sacral nerves, commonly referred to as S2, S3 and S4 respectively. Electrical stimulation of these various nerves has been found to offer some control over these functions. Several techniques of electrical stimulation may be used, including stimulation of nerve bundles within the sacrum.
The sacrum, generally speaking, is a large, triangular bone situated at the lower part of the vertebral column, and at the upper and back part of the pelvic cavity. The spinal canal runs throughout the greater part of this bone. It lodges the sacral nerves, and is perforated by the anterior and posterior sacral foramina through which these pass out.
Several systems of stimulating sacral nerves exist. For example, U.S. Pat. No. 4,607,639 to Tanagho et al. entitled "Method and System for Controlling Bladder Evacuation" incorporated herein by reference, and the related U.S. Pat. No. 4,739,764 to Lue et al. entitled "Method for Stimulating Pelvic Floor Muscles for Regulating Pelvic Viscera" also incorporated herein by reference, disclose implanting an electrode on at least one nerve controlling the bladder. In one embodiment the electrode is percutaneously implanted through the dorsum and the sacral foramen of the sacral segment S3 for purposes of selectively stimulating the S3 sacral nerve. The electrode is positioned using a hollow spinal needle through a foramen (a singular foramina) in the sacrum. The electrode is secured by suturing the lead body in place. U.S. Pat. No. 4,569,351 to Tang entitled "Apparatus and Method for Stimulating Micturition and Certain Muscles in Paraplegic Mammals" incorporated herein by reference, discloses use of electrodes positioned within the sacrum to control bladder function.
Typically electrical stimulation of the nerves within the sacrum is accomplished by positioning a lead having at least one electrode at its distal end through a foramen of the sacrum and proximate the nerve. Of course to reliably exercise nerve and thus bladder or bowel control the electrode must remain anchored in its intended location.
Movement of the lead, whether over time from suture release, or during implantation during suture sleeve installation, is to be avoided. As can be appreciated, unintended movement of any object positioned proximate a nerve may cause unintended nerve damage. Moreover reliable stimulation of a nerve requires consistent nerve response to the electrical stimulation which, in turn, requires consistent presence of the electrode portion of the lead proximate the nerve.
Past leads have been anchored through the use of one or more suture sleeves. Specifically the suture sleeves were tied or sutured about the lead, as is well know in the art, and further sutured to the tissue proximate the sacrum.
This type of anchoring system, however, has several drawbacks. First the sutures may only be tied to the tissue surrounding the sacrum. That tissue, however, is relatively weak and only one or two sutures may be placed through it. Even then the fixation of the lead is less than wholly reliable. In addition, while the suture sleeve is being positioned and sutured to the tissue, the lead may move from the optimal site.
The U.S. Pat. No. 4,569,351 to Tang, discussed above, featured electrodes positioned and fixed to the sacrum through use of a holder. The holder features a hole through which the electrodes extend. Electrode access to the sacral nerves is achieved by the drilling of holes. The holder is rigid, preferably made from a non-conductive, molded material, such as methyl-methacrylate. The holder is fixed to the sacrum through a set of screws. This holder design, however, is less than wholly satisfactory. For example lead implantation is not satisfactorily provided. Specifically, because electrodes extend a fixed length from the holder, once they have been tailored to length and the holder positioned and mounted to the sacrum, the electrodes cannot be further adjusted. In addition, the rigidity of the holder presents several drawbacks. First, it requires the removal of any bony protrusions in order to provide a substantially flat surface against which the holder is to abut. Second, the rigid holder as well as the upstanding lead position tends to concentrate any bending forces to the section of the lead near the holder. As may be appreciated, concentrated bending forces and the resultant increased strain to the lead may result in lead fracture.